Physical vapor deposition, or sputtering, is a commonly used process for depositing material on a substrate. The material to be deposited is contained in a target generally disposed above the substrate to be coated, all in a vacuum chamber. A gas is provided to the chamber, and an electric potential applied to ionize the gas into a plasma. The ions are accelerated toward the target by a magnetic field provided by permanent magnets disposed in a convenient relationship to the target. The ions collide with the target, dislodging particles that fall onto the substrate below.
Deposition by sputtering is generally non-uniform for a variety of reasons. Density of the plasma may be affected by geometry of the apparatus. The magnetic field may be non-uniform due to variation among the magnets or in the relationship of the magnets to the target. In some cases, temperature variation at different locations on the target may result in non-uniform deposition. As the dimensions of devices and layers formed on substrates grows smaller with the general progression of miniaturization in the semiconductor industries, tolerance for non-uniformity diminishes as well, and other sources of non-uniformity, some of which may emanate from nature itself, must be managed. Thus, there is a continuing need for apparatus and methods for dynamically adjusting deposition rate profile in a sputtering process.